1. Field of the Invention
The present invention relates to toners for use in color copying machines such as electrophotographic systems and, more particularly, to photosensitive microencapsulated toners which are cured on exposure to light at a specific wavelength.
2. Description of the Related Art
Known color copying machines used with microcapsules can be broadly classified into two categories including electrophotographic systems and transfer development systems.
The electrophotographic systems make use of microencapsulated toners, wherein ink components are encapsulated, as disclosed in, for example, U.S. Pat. Nos. 3,788,994, 4,016,099 and 4,497,885, Japanese Patent Publication No. 51-35867, Japanese Unexamined Patent Publication Nos. 51-132838, 56-119138, 57-202547, 58-176643, 60-57859, 60-227161 and 63-32560, European Unexamined Patent Publication Nos. 88,566 and 418,851.
In color copying machines, four color toners including yellow, magenta, cyan and black toners are used to make images of the respective colors on a photosensitive material. The resultant image-wise toners are transferred to a material where images are to be transferred. The toner-transferred material is heated or pressed to fix the toners thereon.
On the other hand, transfer development systems make use of toner encapsulating photosensitive resins and dye ingredients as set forth, for example, in U.S. Pat. Nos. 2,548,366, 3,775,424, 3,864,400, 4,399,209, 4,085,648, 4,399,209, 4,440,846, 4,416,966, 4,554,235, 4,576,891, 4,587,194, 4,891,299 and 5,005,028 and Japanese Unexamined Patent Publication Nos. 57-124343, 57-179836, 57-197538, 62-162147 and 62-209444.
In color copying machines, three types of microcapsules are used, in which three dye precursors, dyes or pigments of yellow, magenta and cyan colors are, respectively, contained. The respective microcapsules have the following characteristics. The microcapsules containing a cyan chromogen are rendered solid upon exposure to light at a wavelength of approximately 650 nm (red light). On exposure to light at a wavelength of approximately 550 nm (green light), the microcapsules containing a magenta chromogen are rendered solid. Likewise, on exposure to light at a wavelength of approximately 450 nm (blue light), the microcapsules containing a yellow chromogen are rendered solid.
The uniformly coated sheet of these microcapsules on a support is applied with image-wise red, green and blue light radiations at once or after color separation. Hence, a latent image is formed. Thereafter, uncured microcapsules are ruptured by application of pressure or heat so that the encapsulated chromogens are transferred to a material on which a color developer has been coated.
In the electrophotographic systems used with the microencapsulated toner, however, four color toners have to be used, which in turn requires four toner tanks. This results in the apparatus being expensive. Moreover, four transfer steps are essential for one material where images are to be transferred, with the attendant disadvantage that color shift easily occurs.
On the other hand, transfer development systems are advantageous in that the number of steps is smaller than in electrophotographic systems, because analog exposure to light is possible in transfer development systems. However, since transfer development systems need photosensitive microcapsule-coated sheets and developer-coated materials, these systems consume an undesirably large quantity of materials. This raises copying costs. In addition, since the photosensitive microcapsule-coated sheet has to be kept in a cold and dark condition, a burden is placed on users in securing its storage space. Like once-through ribbons for thermal transfer, the photosensitive microcapsule-coated sheets have portions which are not reused after copying, which raises the possibility that a substantial portion of the sheet will be wasted.
Japanese Unexamined Patent Publication No. 4-249250 has proposed photosensitive microencapsulated toners which solve all of the above problems.
Nevertheless, in view of the recent trend toward higher speed operation of copying machines, existing photosensitive microencapsulated toners are not satisfactory with respect to their sensitivity. In particular, there is a demand for improving the sensitivity of microcapsules which are sensitive to light at a wavelength of approximately 650 nm (red light).